Understanding the transmission pathways of influenza and other emerging infectious diseases is essential for assessing risk, providing effective interventions, and minimizing public fear of epidemics and pandemics. Very little information is available on the number and size of particles generated by infected persons, in part due to the limitations of conventional air samplers. For example, conventional air samplers do not efficiently capture fine particles and do not maintain the viability of captured microorganisms. Therefore, a need exists for air samplers that efficiently capture fine particles and maintain the viability of captured microorganisms.